1. Field of the Invention
The present invention relates to a multicolor printing press, in which a plurality of printing sections are arranged in vertical alignment in spaced part relationship to each other. More specifically, the invention relates to a multicolor printing press which is featured in capability of adjustment of rotational phase of a plate cylinder carrying a printing plate for adjustment of register position in circumferential direction of the plate cylinder. The invention further relates to a multicolor printing press which is particularly suitable for printing on a uniform kind of web paper, such as a newspaper.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 3-1946 discloses a construction of a multicolor printing press, in which a plurality of printing devices are vertically arranged in spaced apart relationship. The above-identified publication also discloses a register position adjusting means which minimizes register error of printing patterns between the printing sections. The printing register position adjusting means in the shown construction comprises at least means for adjusting along axial direction of each plate cylinder relative to a corresponding blanket cylinder, for each of the printing sections.
The prior art disclosed in the above-identified publication is designed for compensating expansion of a web paper due to variation of humidity, on which printing of printing pattern is performed, by allowing adjustment of register position in the transverse direction relative to the feed direction of the web paper. Such technology should provide certain extend of gain in certain accuracy in the transverse register position. Particularly, such technology is effective when a various kinds of web papers are used for printing.
In contrast, in case of multicolor printing of newspaper, since specific kind of web paper is used. The variation in the width direction of the web paper due to variation of humidity is substantially constant. Therefore, in such case, transverse register position can be preliminarily adjusted by adjusting the position to place the printing plates on the plate cylinder to compensate the width variation based on expected magnitude of variation of the width. This makes the transverse register position adjustment less important than that in the former case.
On the other hand, in multicolor printing of the newspaper, the contents, topics, to be printed have on the newspaper have to be differentiated for local area to which the newspaper is to be delivered. Also, it is frequently experienced in making newspaper that necessity of rearrangement of news is caused for newly occurring news. Therefore, in the printing station of newspaper, the printing plates on the plate cylinders are often rearranged or replaced. Re-arrangement or replacement of news is taken place by interrupting printing operation. After completion of re-arrangement and/or replacement of the printing plate, printing operation is resumed. During this procedure, non-uniform tension is exerted on the web paper in paper feeding direction. This tends to cause variation of expansion ratio in the longitudinal, i.e. paper feeding, direction to cause register error in the printed color images to degrade quality of printed image. In the prior art, substantial load is thus added for performing fine adjustment of the register position of the plate cylinder in its circumferential direction. Furthermore, for correcting register error, substantial amount of paper should be wasted.